Hard expanded rubber



- cumbersome and expensive and results in a high e gred e entering i 1Jhe Composition percentage of rejections in manufacture. are as follows, e pr in relative Parts y 20 We have discovered that the addition of rub- Weight:

ber dust to the composition of the gas expanded n by rubber results infa product having a surface weght which may be highly polished. The density of 100.000

the resultant expanded rubber is twenty to forty 233:3? 50.000 25 pounds per cubic foot depending chiefly upon Whiting 30.000 the percentage of rubber dust used. The gas ex- Light calcined magnesia 16.000 panded rubber is produced in a manner similar Reogen 1.250 to that described in the pending appli ation of Zinc 7.000

to Scott, Robert and Peel, Ser. No. 717,550 filed Petrolatum I": 4.350

I March 27, 1934 except for the addition of the Carbon black 2.000 rubber dust. The dense expanded rubber may be Paramn wax 3.000 used for readily molding articles having compli Ageme powdgr 1250 cated shapes since during the-final curing stage mphenyl 'm .625

86 appreciable-volume expansion takes place to com- Mercaptobenzothiazole .200 pletely fill irregular molds.v The ordinary type Hard rubber dust 50.000 .of hard rubber does not expand in this manner but must be entirely "shaped before being placed a 266,175 in the mold for final curing. Y r

40 y The hard expanded rubber produced aecord- The ingredlents are prepared and the rubber 40 f Patented oer. 24,1930 I v I 2,176,946

Products, Inc., New York, N. Y.,.a-c'orporation of Delaware i No Drawing. Application January 2, 1938,

Serial No. 57,248 g 3 Claims. (c1. 18- -53) This invention relates to dense expanded rubable surface so that a high gloss may be prober having a hard .polishable surface. duced thereon;

Hard rubber is used to make many articles 7 A further object of this invention is to provide where a hard polishable surface is desired. Ora novel hard rubber which is expandible within 5 dinary' hard rubber has a density of about; the mold so that hard rubber articles having ir- 5 ninety to one hundred pounds a cubicfoot. Such regularities of surface and contour may be readrubber does not expand so that it is relatively ily manufactured.

difficult to manufacture articles having surface A further object of this invention is to provide and contour irregularities. Gas expanded rubber a novel hard rubber of approximately half the 10 lends itself to ready expansion tofill complidensity of ordinary hard rubber at a consider-l0 cated molds. However, such material has hereably lower cost. I tofore been relatively light in weight being of Still another object of this invention is to the order of six to eight pounds per cubic foot, provide a novel expanded hard rubber of relabut had no hard polishable surface It has been tively high tensile a d p ssiv t 16 proposed to add a layer of ungassed rubber onto These and other objects of our invention will 15 thoroughly gassed stock before placing it in the become pp in e fellowing s p mold for final curing in order to secure a hard of a preferred composition illustrating our inpolishable surface. However, such a method is vention.

product is manufactured in a manner similar to that described in the application Serial No. 717,- 550 supra. The addition of the hard rubber dust or ebonite dust as it is generally known is the basis ing to the present invention'may be used for practically any application that the well known hard-rubber is used for; for example,sheet stock, toilet seats, ice cream can covers, electrical incture of sulation and all othervarticles requiring great g g g g ifgggggg gfiggg iggi z gg f be tensile and compressive strength The dense carried out in any suitable manner already esexpanded rubber comprises less than half the t u in t t, 3 materials pa to Ordinary hard m The sheets of' rubber are masticated and the her a d ay ac y be manufactured at 9. ingredients are mixed on the mill until they 50 considerably lower cost than hard rubber. are completely dispersed to produce a rubber Accordingly, an object of this invention is to dough. The dough is then calendered or tubed provide a novel, dense, expanded gassed rubber. dependent upon the shape of the article to be i Another object of this invention is to provide a. made. After eighteen hours or less, the dough is novel, gassed, expanded rubber having a polishplaced in an autoclave. As is well known in the 56 pound per square inch pressure of steam is' ad .mitted in the heating coils for one and a half ,hours. The apparatus is then permitted to-cool 10 down for one hour (no water on) and then cooled fortwo and a half hours with circulating water flowing through the autoclave pipe structure. The gas pressure is then' withdrawn from the autoclave and the gassed dough is removed. The

' 15 gas at a high pressure isadsorbed by the rubber dough and the heat in the. autoclave semi-cures the dough so that upon its removal from the autoclave, the gas is retained in the dough in individual cells.

.20 The gassed rubber dough is then roughly shaped before being placed into the molds. The mold may have irregular shapes or contours since the rubber dough will expand to fill them during the final curing process. The. rubber .25 dough is placed in the mold which is placed into a platen press. The press maintains sufiicient pressure on the mold to counteractthe expansive forces generated by the expanding rubber within it so that it may conform to the desired molding .30 .cr shape. The platens are steam heated so that the dough within the mold may be finally cured:

Forty pounds per square inch of steam-is applied for one-half hour followed by the applicationof ninety pounds per square inch steam pressure for '35 one and a halfhours. The platen press isthen I cooled, down as quickly as possible tofcomplete the cure. The product is removed from the mold only when the moldis; thoroughly cooled. The

rubber dough is compounded so that when it is plaee d in the autoclave. under high pressure of an inert gas, it will be partially cured suificientlyto retain a large amount of the.adsorbed or occluded gas after the gas pressure is released and yet be sufiiciently uncured to possess expandibil- '5 ity and mobility for properly filling the mold during the final curing stage. The process is based upon the formation of a myriad of independent as cells within the dough by theinert gas at a high pressure. Each minute cell expands in size 5 according to the contained pressure of the gas and according to the tensile strength and percentage elongation of the. dough. During the heating of the final curing stage, the entrappedgas of the individual cells exerts great internal 55 pressure, furtherexpanding the cells. At least twenty-five per centincrease involume occurs durin the final curing stage and the quantity of dough placed in the mold should permit proper expansion Jthereof. Overexpansion should be so avoided to prevent rupturing of the gas-cells during the finel expansion so as to produce a hroduct having an individual gas cellular strucure. v

The hard rubber dust is completely dispersed in as this stock and is vulcanized during the final curing stage. The. resultant finally cured product lends itself readily to grinding down and polishing operations necessary to produce a high gloss,

on its surface. This product maybeproduced 70 having a skin thickness of of an inch or more. The thickness of the skin "depends upon the density of the stock, a denser stock producinga thicker skin. .By the term skin is meant that outer portion of the product where the gas, cells 75 have been ruptured to produce a non-porous,

2,176,946 non-cellular layer or skinon the product. There is hydrogen sulphide gas generated during'the curing process, adding substantial increase to the internal pressure of the stock .to aid in further expansion thereof. 1 5 The polishing ispreferably accomplished by first grinding and then bufilng as is well known to those skilled in the mechanical arts. Three grinding operations, *with abrasives, coarse, medium and fine, are performed successively; the final polishing operation is performed with a buffing wheel to produce a high gloss on the surface of the product.

The hard rubber dust added to the gas ex-- panded rubber and vulcanized therewith, acts as a filler having the same abrasive co-efiicient as the remaining stock excepting the mineral fillers. When a given area is to be polished, it is necessaw for the surface to wear down evenly or smoothly under the action of the abrasive. Hard rubber dust is used because the resultant product will. have a homogeneous abrasive co-efiioient so that a homogeneous finish may be produced, thereon. If, coarse mineralfillers are used to any great extent, the abrasive will tear out the pocketed mineral fillerv duringthe polishingprocess to produce pitted marks. Accordingly. the use of coarse'mineral fillers should be avoided but the specified mineral ingredients should be finely round so that a high gloss may be produced upon the surface of the product. The rubber product of the present invention may be made having a density of twenty to forty pounds per cubic foot to produce a hard, dense, expanded rubber having relatively high tensile and com-.

pressive strength. Since ordinary hard rubber products weigh" from ninety to one hundred pounds per cubic foot, the product of this invention may be produced at a substantially lower cost per cubic foot. The hard expanded rubber 40.-

according to this invention, may be substituted for ordinary hardexpanded rubber in practically all applications. It possesses the necessary strength, it may be readily highly-polished and may be fabricated into complicated shapes as a 'result of its marked expandibility within the mold. Some of the articles of manufacture which may be made with the dense,- expanded rubber composition are, .for example, sheet stock toilet seats, ice cream container lids, polished panels. 60.

refrigerator doors, electrical heat and sound insulation members and the like.

Although we have described in detail the specific constituents of the preferred form of our product and the ejxact steps of one process for forming the same, it will be obvious that modifications thereof still coming within the scope and spirit of the invention may be made both in the constituent'parts and in the process and we do not intend to be limited except as set forth in the. 60.

following claims. We claim:

1. As an article. of manufacture. a hard and rigid gas expanded rubber structure containing a multiplicity of small sealed cells of gas, said structure containing a substantial amount of hard rubber dust, said hard and rigid gas expanded rubber structure having a density on the orderof 20 to 40 lbs. per .011. ft.

2. As an article of manufacture, a hard and rigid gas expanded closed cell rubber structure with a substantial amount of hard rubber dust at the periphery of the structureadapted to provide a highly polished surface, said hard and rigid gas expanded closed cell rubber structure 76 cu. ft.

3. As an article of manufacture, a hard and rigid gas expanded closed cell rubber structure with a substantial amount of hard rubber dust contained in the periphery of thestructure, said hard rubber dust being adapted to produce, upon polishing, a homogeneous and bright rubber surface, said hard rubber dust being distributed substantially homogeneously throughout the rubber structure and materially increasing the tensile and compressive strength thereof.

- DUDLEY ROBERTS. LESTER S. COOPER. 

